1. Field of the Invention
The present invention relates to a transmission control system used in a facsimile transmission system, more particularly, to a transmission control system having different and improved control codes which are necessary during the transmission so that it achieves a shortened transmission time.
2. Description of the Related Art
Conventional standard high-speed facsimile transmissions have been performed by using G3 transmission control procedures based on CCITT recommendations. The T.30 transmission control procedure used in G3 consists of a control code portion or division transmitted at a transmission speed of 300 bps (bits per second), an image data portion or division transmitted at a transmission speed of 9600 bps. In such a transmission method, the image data division is used with an MR data compression method, and the transmission time is shortened by enlarging the K parameter (insertion pitch of the MR data compression method). However, since this transmission method cannot shorten the transmission time of the control code division, the control division limits the facsimile transmission speed.
FIGS. 1(a) to 1(d) illustrate the operation procedure based on the conventional G3 procedure. FIG. 1(a) shows the normal operation procedure, FIG. 1(b) shows an end procedure for an abnormal operation caused by the failure of the training, and FIG. 1(d) shows a data retransmitting operation procedure caused by the occurrence of many errors in the image data. These operations are explained briefly hereinafter. In the drawings, the wavy arrow mark indicates the tonal signal (sine wave signal, 2100 Hz in the G3 procedure), and the straight arrow mark indicates the command code or response code according to the series code method based on a transmission speed of 300 bps. Moreover, the slanted or hatched arrow marks indicate the transmission of the image data based on a transmission speed of 9600 bps. Reference letter "S" indicates the transmission side of the facsimile system, and "R" indicates the receiving side.
(a) Normal operation procedure
When the 16 Hz calling signal is transmitted from the S side to the R side, the R side responds to the S side with the 2100 Hz tonal signal CED. In succession, the R side responds to the S side using the response code NSF.DIS (NSF indicates a non-standard procedure) indicating the receiving function such as paper size, compression method, and recording speed using a transmission speed of 300 bps. The S side transmits the command code NSS or DCS (where NSS indicates the non-standard operation, and DCS indicates the standard operation) as the control signal indicating the transmitting function and, in succession, the S side switches the modem from 300 bps to 9600 bps, and transmits the training data having an "0" signal for the predetermined term or time period. In the R side, when the training data is received as the normal "0" signal, the R side transmits the response code CFR, indicating completion of the preparations for receiving. According to the response code CFR, the S side transmits one page's amount of the image data using the 9600 bps transmission speed and, in succession, it transmits the command code MPS indicating continuation to the next page. In this case, since the image data is normally received by the R side, the R side responds to the S side using the response code MCF, indicating normal reception. The S side transmits the image data of the next page and the command code EOP indicating the end of the page to the R side. When the R side confirms normal reception of the image data, the R side responds to the S side with the response code MCF, and the S side transmits the command code DCN, indicating the disconnection of the circuit and the end of transmission.
(b) Abnormal operation procedure
When the image data has been transmitted from the S side to the R side, if the R side cannot normally receive the image data because it has run out of receiving paper, the R side responds to the S side with the response code PIN, indicating an abnormal condition at the terminal. The S side transmits the response code PRi-EOP or PRi-MPS requesting an operator call on the R side, and outputs an alarm by using the operator call, to indicate an abnormal condition, and again transmits the response code DCN, indicating the disconnection of the circuit and the end of the transmission.
(c) Retraining operation procedure caused by failure of the training
When the training data cannot be received normally by the R side, the R side responds to the S side with the response code ETT, indicating failure of the training, and the S side again transmits the training data. When the training data is received normally by the R side, the R side responds to the S side with the response code CFR, indicating completion of the preparations for receiving, and after this time, the normal operation procedure shown in item (a) is performed between the S side and the R side.
(d) Retransmitting operation procedure caused by the occurrence of many errors in the image data
When the image data received by the R side contains errors over a predetermined amount, the R side responds to the S side with the response code RTN. The S side changes the transmission speed of the image data of the next page from 9600 bps to 7200 bps, and informs the R side using the command code NSS, indicating a non-standard operation. After that, the S side again transmits the training data to the R side, and the R side performs the normal operation procedure shown in item (a) after responding to the S side using the response code CFR.
As mentioned above, the conventional G3 procedure is performed by exchanging many different command codes and response codes at a low transmission speed of 300 bps, therefore, the necessary time for transmitting these codes takes several tens of seconds, and takes about one-sixth of the overall transmission time. Moreover, the conventional G3 procedures have problems, in that it is necessary to have training time of from 1 to 2 seconds, and the retransmission when many errors occur is performed after complete transmission of one pages amount of image data, so that considerable transmission time is wasted.